This invention relates to a rear door opening mechanism for a truck and to a truck. body with a rear door opening mechanism.
Cube vans and step-up vans have a walled cargo area closed by a rear door. Typically, the rear door is a so-called xe2x80x9croll-upxe2x80x9d door. A roll up door has a number of laterally elongated rectangular sections which are hinged together. Rollers extending from the door sections are received in guide channels. The guide channels have a lower portion extending vertically from the base of the cargo area and then curve to an upper portion extending horizontally along the inside of the roof of the cargo area. The door is opened by lifting vertically which causes the panels to ride along the guide channels such that consecutive panels cant to a horizontal orientation and are received by the upper portion of the guide channels.
A roll up door suffers from several drawbacks. Firstly, since the guide channels extend along the inside of the roof of the cargo area, the roll up door reduces the effective size of the cargo area. Secondly, the hinge points between door panels can let in water and dust. Additionally, these doors require a fair degree of effort to operate. Further, on the road, vibrations imparted to the segmented door result in nuisance noise. Finally, the segmentation of the door detracts from its appearance and does not facilitate the application of decals to the door.
This invention seeks to overcome these drawbacks.
The present invention provides a four bar linkage between the walled cargo area of a truck and a rear door. This allows use of a rigid rear door. The effective length of the lower link of the four bar linkage is longer than that of the upper link such that the motion of the door can be generally up and over the top of the truck body. An eccentric cam can be joined to one of the upper and lower links with a tensioned spring extending around the cam such that the spring slackens as the door opens. The cam can then be configured so that, as the door is opened, the spring will slacken more slowly initially then more quickly. This allows the door to be moved initially mostly outwardly before moving significantly upwardly and still be effectively counterbalanced throughout its motion.
According to the invention, there is provided a truck body comprising: a walled cargo area; a rigid rear cargo door for closing said cargo area; a four bar linkage having an upper link and a lower link each mounted by a pivot to a side wall of said walled cargo area and each mounted by a pivot to said rear cargo door; and a linear distance between pivots of said lower link being longer than a linear distance between pivots of said upper link.
According to another aspect of the invention, there is provided a rear cargo door opening mechanism for a truck having a walled cargo area comprising: a four bar linkage having an upper link and a lower link each for mounting by a pivot to a side wall of said walled cargo area and each for mounting by a pivot to said rear cargo door; a linear distance between pivots of said lower link being longer than a linear distance between pivots of said upper link; an eccentric cam joined to one of said upper link and said lower link; a spring for extending around said eccentric cam such that, in use, said spring is in tension and as said rear cargo door opens, said spring slackens; said eccentric cam configured such that, in use, as said rear cargo door is opened, said spring slackens more slowly proximate a closed position of said rear cargo door than proximate a point midway between a closed position and an opened position of said rear cargo door.